The present invention relates to a photosensitive member having an amorphous silicon photoconductive layer.
Amorphous silicon (hereinafter referred to as a-Si) and/or amorphous silicon:germanium (hereinafter referred to as a-Si:Ge) are superior to the conventional photosensitive members free of environmental pollution and having excellent characteristics in thermal resistance, surface hardness, abrasion resistance as well as in light sensitivity characteristics. Particularly, a-Si/a-Si:Ge laminate-type photosensitive members have an increased absorption coefficient to long wavelength light because the a-Si:Ge layer has a small energy gap as compared with the a-Si layer, and as a result, an effect of extending the photoconductive characteristics to the long-wave region, can be expected.
But, this small energy gap of a-Si:Ge reversely makes the dark resistance of a-Si:Ge smaller than that of a-Si. Consequently, when a-Si and a-Si:Ge are laminated, there occurs a problem that a charge relating capability required for a photosensitive member lowers. While, in incorporating Ge in a-Si for the purpose of sensitization toward long wavelength for the a-Si:Ge layer of a constant thickness, low Ge concentrations make the absorption of long-wave light so poor that great sensitization cannot be expected. And, high Ge concentrations ensure sufficient absorption of the light, but decrease the .mu..tau. of generated carriers to cause a reduction in mobility. Also, in the case of a definite Ge concentration, a small thickness of the a-Si:Ge layer makes the absorption of long-wave light so poor that great sensitization cannot be expected. And, a too large thickness ensures sufficient absorption of the light, but makes the .mu..tau.E of generated carriers smaller than the thickness of the a-Si:Ge layer to cause a rise in residual potential. Consequently, in order to attain sensitization toward long wavelength most effectively, it is necessary to design so as to keep optimum balance between the Ge concentration and the thickness of the a-Si:Ge layer.
On the other hand, a-Si and a-Si:Ge have a defect that they are too low in the dark resistance to use them as a charge retaining phoconductive layer. For this reason, there is a proposal of increasing the dark resistance by incorporating oxygen and carbon or nitrogen [Japanese Patent Application Kokai (Laid-open) Nos. 145539/1979 and 145540/1979]. But, this proposal has a defect that the light sensitivity characteristics become poor with an increase in the content of the additive, which means that the content needs to be fairly limited. For this reason; there was proposed a method to improve the charge retaining capability by forming a high-resistance a-Si layer containing oxygen and nitrogen or carbon in large amounts on the electroconductive substrate, thereby inhibiting injection of charges from said substrate [Japanese Patent Application Kokai (Laid-open) Nos. 52180/1982, 58160/1982 and 63546/1982]. Surely, the photosensitive member obtained by this method acquired an improved charge retaining capability, but it has the a-Si layer containing oxygen and nitrogen or carbon in large amounts on the electroconductive substrate, so that some of the carriers generated in the photoconductive layer cannot move out to the substrate to cause the rise in residual potential to generate the so-called "fog" on the image.